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Damping of high-lying single-particle modes in heavy nuclei
Institution:1. Center for Advanced Studies in Chemistry, North-Eastern Hill University, Shillong 793 022, India;2. Department of Chemistry, University of Washington, Seattle, WA 98195, USA;1. Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, USA;2. Department of Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, TN 37232, USA;3. VA Tennessee Valley Healthcare System, Nashville, TN 37212, USA;4. Department of Chemistry, Tennessee State University, Nashville, TN 37209-1561, USA;1. Faculty of Environmental Sciences, Czech University of Life Sciences, Prague, Kamýcká 129, 165 21, Prague 6-Suchdol, Czech Republic;2. University of Chemistry and Technology, Prague, Technická 5, 166 28, Prague 6, Czech Republic;1. Faculty of Applied Chemistry and Materials Science, University POLITEHNICA of Bucharest, Polizu Street No 1, 011061, Bucharest, Romania;2. Laboratoire de Chimie, CNRS, Université Claude Bernard, ENS-Lyon, 46 Allée d''Italie, 69364 Lyon cedex 07, France
Abstract:The recent experimental and theoretical results on the damping of high-lying single-particle modes in heavy nuclei are reviewed. In one-nucleon transfer reactions these states manifest themselves as broad “resonance”-like structures superimposed on a large continuum. The advantages and the limitations of the transfer reaction approach will be presented using the results from neutron and proton pick-up and stripping reactions. The problem raised by the subtraction of the underlying background, the assumptions made to describe the reaction process and the method used to extract the strength distributions are presented. The existing empirical systematics is summarized for nuclei ranging from 90Zr to 208Pb.The theoretical approaches used to explain the damping of the high-lying single-particle modes are based on the coupling between collective and single-particle degrees of freedom. In a first step the bare single-particle mode is spread over several doorway collective states due to the interaction with surface vibrations. In a second step the doorway states spread their strengths over many other degrees of freedom. These two steps of the damping mechanism are discussed in detail within the framework of the quasiparticle-phonon nuclear model. A large-scale comparison between the measured and calculated average energies, spreading widths and spectroscopic strengths of the high-lying single-particle (hole) states in heavy nuclei is presented. The systematic features of the damping (energy, angular momentum and isotopic dependence) are discussed. Recent advances of the experimental approaches, such as the γ-decay of the high-lying states or the use of heavy-ion transfer reactions at intermediate energies, are outlined.The detailed study of the damping mechanism of high-lying single-particle modes reveals new features and leads us to a new field in nuclear structure: “the spectroscopy of inner and outer subshells”.
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